Smart hubs and the architectures of such smart hubs are described in an article "Designing a Third Generation Hub Meets the Network Challenge" by Bob Roman in "Computer Technology Review", Vol. 11, No. 16, February 1992, pp. 25-29. Problems have been encountered with regard to high speed and cost effective communication for such hub backplane communication systems. Particular problems have been encountered with regard to collision detection and slot identification associated with CSMA/CD protocols based on bus topology.
Collosion detection time is a major component with regard to 802.3 protocols and, to a great extent, defines a performance level. Various different methods are being used for minimize collision detection time. Such methods often involve large pieces of collision detection hardware integrated into the hub modules.
One of such methods is based on slot comparison during transmission. This method also requires additional pins to be provided on the backplane segments for slot identification (slot ID). With such a method, the number of slot ID pins is defined as binary log N, where N is the number of nodes, communicating over a backplane segment. For example, a backplane segment with 32 nodes will require 5 pins for the slot ID. Such an arrangement is necessarily a drawback with regard to cost and simplicity of the overall system implementation (including hardware and software).